Although the present invention has application to the installation of trusses over substructure assembled on-site, it is particularly suited for use in building construction utilizing prefabricated substructure units, such as preassembled wall components.
In a typical such construction, a plurality of prefabricated wall panels, each comprising for example lightweight galvanized C-channel sheet steel top plate, base plate and studs welded together and joined to wall sheathing, are erected end-to-end about the peripheral margin of a concrete slab or other suitable supporting foundation. Trusses, such as inverted V-shaped trusses for establishing the framework for roofing, are then positioned above the panels at standard intervals and secured thereto. Typical trussing in such prefabricated assembly comprises planar configurations of joined top chord, bottom chord and webbing interconnecting the two, with a centrally located vertical king post serving to establish the high point or ridge of the roof. The trusses are lifted one-by-one into position above the assembled wall panel substructure, beginning at a gable end. Each truss is shifted back and forth on the top plates of the underlying wall panels until centered, then toe-nailed or riveted into fixed position after vertical leveling. During the placement process, adjacent king posts are cross braced by means of diagonals, typically extending from the top of one king post across the center of a second post to the bottom of a third post.
Each truss must be carefully leveled and positioned in order to provide the proper underlayment for sheathing and other standard-sized roof covering materials. Where plywood sheathing is used as flooring for roofing, the trusses are typically set so that sheathing is passed from the centerline of the top chord of one truss to the centerline of the top chord of another truss, with usually one truss in between, the sheathing running crosswise over the trusses. The bottom run of sheathing must be carefully positioned so that the overhang, if any, is in alignment and so that the remaining boards will be properly situated. Considerable skill and effort, to say nothing of time, is expended in achieving the required installation. Where non-prefabricated materials are utilized, the installation is accordingly even more complex.
For some construction, the top chord extends beyond the wall line to a point to be covered by fascia material, and the underside of the overhang is blocked with soffit covering. Where this is undertaken, a soffit framework is normally attached to the overhanging tail or eave ends of the top chords, necessitating the expenditure of additional skill and effort.